Writing instrument



FIG. 1 is a front elevational view of a writing instrument showing my new design;

FIG. 2 is a right side elevational view thereof with the top member and writing point in extended positions;

FIG. 3 is a rear elevational view of FIG. 1;

FIG. 4 is a bottom plan view; and

FIG. 5 is a top plan view. 

The ornamental design for a writing instrument, as shown and described. 